Increased use of ultrasound as a medical diagnostic modality makes it imperative that potential hazards to the patient be identified and understood. Such detailed information on the interaction of ultrasound and living systems is not presently available. The primary goal of this research is the establishment of safe limits for this use of ultrasound as it is presently employed, and anticipated to be used, in clinical medicine. These goals will be accomplished through the detection of histopathological and functional changes induced in selected mammalian tissues. Experimental animals will be subjected to various irradiation modes currently employed, or anticipated to become operational, in clinical practice, (viz., c.w. doppler, pulse-echo, transmission holography). Dosage conditions for the various irradiation modes will be increased until a structurally and/or functionally detectable end- point is observed. The ultrasonic dosage levels which produce identifiable tissue changes will be studied for the reproductive organs, the developing mammalian embryo, nervous tissue and blood vessels, and safe dosage limits of operation will be established for each. Few previous investigations have been concerned with ultrasonic toxicity, i.e., the upper limits of safety for which reliable criteria for completely safe limits can be established, but rather with fundamental biophysical interaction mechanisms. It is the intent of the proposed research to aid in establishing these limits and to begin the accumulation of the much needed toxicity information.